ARTICLE TOOLS

Gerbillus pyramidum and G. allenbyi are primarily granivorous, nocturnal rodents that are sympatric over many sandy areas of the Negev Desert. However, in their overall distribution, G. pyramidum occurs in extreme desert areas whereas G. allenbyi does not. We measured the average daily metabolic rate (ADMR) of gerbils of each species when they were offered pelleted diet. Given the difference in their distribution, we reasoned that the more xeric G. pyramidum would have lower ADMR than G. allenbyi; however, given the similarity in their diets, we reasoned that their ADMRs would be similar. The latter alternative was supported. ADMR of G. pyramidum (body mass = 31·9 ± 5·4 g) was 427·1 kJ·kg−0.75·d−1, 58% of that predicted for a rodent of its body mass; whereas ADMR of G. allenbyi (body mass = 22·3±2·3 g) was 387·7 kJ·kg−0.75·d−1, 49%) of that predicted. On the basis of these results, we suggest that factors other than their ADMRs are important in determining their geographical distribution.